An application device of this kind has been known for a long time. Reference is made for example to DE 1 398 907 A1. This solution indeed, does not relate to dental materials but a hand lotion, however, comprises a cartridge and an application nozzle. Between the two components a positive locking is provided, and openings are formed for the ventilation and exhaust of the cartridge. The openings can be provided either at the cartridge or at the application nozzle.
One disadvantage of a solution of this kind is the fact that also material that is to be pressed, can exit or escape there. This may be relatively uncritical in the case of a hand lotion, since the material exiting there after the exhaust has been realized by exerting pressure on the piston of the cartridge, can be removed in a relatively uncomplicated manner.
On the other hand, however, dental materials are often of high quality such that losses are to be avoided. In the raw condition, dental materials frequently also comprise reactive substances. Free radicals in monomers of light-curable dental materials are to be taken into account, but also chemical compounds used in pastes that only achieve a stable and non-reactive condition by burning them in a dental burning oven.
In this respect, in order not to realize a contamination especially in the region of the application nozzle, it has also become known to realize the exhaust in the piston region. Especially with expendable or single-use nozzles this is uncritical, since if dental material escapes at this location, it remains relatively protected in the cartridge region between the plunger of the piston and the piston handle. Such a solution is obvious for example from DE 200 10 417 that also provides for a specific valve.
This solution, however, is complicated and can basically only be employed reasonably if the cartridge is kept suspended such that the amount of air remaining in the dental material appears adjacent to the piston plunger.
With dental materials, on the other hand, the problem arises that also in the region of the application nozzle the inclusion of air pockets or bubbles should be avoided if possible. Such air pockets or bubbles lead to a significant deterioration of the restoration result, since in the case of air inclusions the dental material is typically weakened such that cavities develop that are prone to contamination. If necessary, the aesthetic appearance of the restoration part needs further treatment or finishing, too.
Accordingly, in order to possibly avoid air inclusions of this kind, it has been proposed to keep the cartridges suspended and when connecting the application nozzle to pay attention to the fact that no air inclusions possibly remain. Typically, a collar of the application nozzle extends into the cartridge. Especially in a collar arrangement of this kind there is the danger of air accumulating behind the collar, more precisely at the highest position of the cartridge or, as the case may be, air being entrained if the piston is actuated.
Even in the case that a collar of this kind is not provided, however, there is the possibility that air inclusions remain which are then entrained. In this connection it has already been proposed to impart a truncated conical construction to the upper end wall or front wall of the cartridge. In the case of a rather viscous dental material, however, the possibility exists that the dental material or mass already extends at least partially into the nozzle grommet or spout of the application nozzle and thus closes off against the edge at the transition region between the conical part and the grommet or spout. This may result in air inclusions, too, in which case the danger arises that the air inclusions are entrained.